Aluminas have many applications. They are used, for example, as selective adsorbents, catalysts and catalyst supports. It is desirable to have a product with a narrow pore size distribution range for many of these applications. Hydrous alumina or alumina gel generally formed by adding ammonia or other alkaline material to a suitable aluminum salt. The porosity characteristics of the alumina are determined, in some instances, by the method of preparation. The products generally have an extremely wide pore size distribution range with the pores between 150 and 1,000 to 2,000A.
U.S. Pat. No. 3,322,494 to Magee et al. describes a process for preparing alumina having a pore size distribution in the 1,000 to 2,000 A range by adding small amounts of microcrystalline cellulose to an ammonia solution, mixing the ammonia with an aluminum salt solution, aging the mixture, filtering to remove the precipitate, followed by drying and calcination steps. U.S. Pat. No. 3,325,247 to Magee et al. describes a process for producing gamma alumina having a pore size distribution in the 500 to 1,500A range by preparing a polyethylene glycol-ammonium carbonate solution and mixing this solution with an aluminum nitrate solution following aging, filtering and calcination steps. U.S. Pat. No. 3,853,789 to Warthen et al. describes a process for preparing strong, attrition resistant alumina extrudates having large mercury pore volumes by extruding specific proportions of aluminum monohydrate and gamma alumina powders.
The importance of pore size distribution in catalysts designed to convert the noxious components in auto exhaust gases to innocuous entities is discussed in some detail in U.S. Pat. No. 3,661,806 of Briggs et al. This reference discloses a process for preparing a catalyst support that has a large percentage of the pores in the greater than 3500A size range with a substantial portion in the size range less than 120A. The large pores of this specific size are no longer of primary importance since their function was to trap the lead salts in the auto exhaust gases. The gasoline currently being used with the auto exhaust conversion catalyst systems is lead free, thus, eliminating the need for the extremely large pores, but certain microporosity is required for activity retention.